Method of preparing a viscous cellulose acetate solution



Feb. 13, 1951 R. w. BRulNs ET AL 2,541,012

METHOD OF PREPARINO A vIsOOUs OELLULOSE AOETATE SOLUTION Filed Aug. 6,1947 SOAVE/vr Z0 SUPPLY 19 l v. I

1 HEATER ci i I BR//vE-JAC/rfrf l I l I REL/EF VALVE L co/vof/vsfkO; i gfg l I l i E: li 3 M f 7i J7// l l i I l To 70 sro/@AGE VACUUM PUMPRICHARD W. BR UIN S WALKER .F`. HUNTER.JR.

ATTORNE 5 Patented Feb. 13, 1951 METHOD 0F PREPRING :A VIS COU S CELLU-LSE SACETATE SOLUTION Richard `W. Bruins and Walker F. Hunter, Jr.,Rochester, N. Y., assigno'rs to Eastman Kodak "Company, Rochester, N.sa, .corporation of New dersey Application-Auguste, lefimserialno.766,851

(o1. insg-1198 'This invention relates to :a method vof cooling hotviscous 'cellulose vester solutions which `atnormal temperatures arehighly viscous and which are employed in mak-ing `photographic filmbase, yarn, thin sheeting .and the like.

The `manufacture of vphotographic 'lm base `particularly lrequires thatthe casting 'solution or clopes which `are cast into the base 'sheet beof `uniform "composition and `loe free of impurities. Similarly in'spinnin'gacetateyarn through microscopic spinnerettes thesoinningsolution mustbe free from impurities and undissolved ester vparticles.lIn order .to 'obtain Aa 'uniform solution 'the 'solvent and the`cellulose ester, or resin as the case may be, Yareoften 'heated 'torelatively high temperatures to induce solubility. 'Solutions are alsofiltered to 'remove :any undissolved materials or foreign matter 'whichmay mhe lpresent. Since the solutions atnormal .atmospheric temperatures'are highly lviscous moderate heatingis generally employed to reducetheir "viscosity `'to facilitate iltering. For example, ra'solution'having a viscosity of 60,000 cps. at 100 F. "has a viscosityof 3000 cps. at 200 F. and"750 cpsiatzlifl" F. Hence, 'if `one "couldYheat lthe usolution to 4such raised 'tempe'ratures filtration rates'100 times those emoloyed at present 'during filtering would 'bepractical. After the solution is 'heated and filtered, considerable'eiort must be .expended to cool ythe 'hot iiltered solution down Ato atemperature so `that it maylbe employed"substantially "at the,predetermined `viscosity "in the iilm casting process. Oi course :thehigher 'temperature .employed increases the problem'andldiliiculty ofsuch cooling. The lproblem is complicated V*by the fact that `as thesolution cools its `A`viscosity Tincreases and, therefore, the rate oiAcooling proportionally diecreases lwhen employing conventional `he`atexchangers. 'Usually Ythe 'cooling Yof 'the hot viscous solution lisaccomplished :by 4some Armadilication of shell and tube coolersVwhich-are Ioperated at ylow rates 'because `'of 'the increase -in theviscosity of .thematerial as it is being coeleizl.` The pressure dropthrough such a cooler is usually A.iaigh and multiple sections are usedto reduce the apressure drop. These coolers have given difficulty and.are vcostly Vto install 'and ser-vice. 'When `employing -certainsolutions -fof `Ivory high viscosity, the l section of the .1 solutionvadjacent the `cold Wall .of the tube lhardensztvhile only the centersection remains flowable. Eventually lall ow may fcease. .An object,thereforeo'i the 'present :invention is an improved and rapid method ofcooling ho iuids `and solutions. n

Another object isla .niethodlot continuously .eoolinghot viscous.l'fluids and solutions.

Another object of the invention is a method of cooling hot viscous`fluids `which is substantially not vaffected lby viscosity increases ofthe -fluids during `cooling.

Y'Still another object of the invention 'is to provide fa method ofsimultaneously cooling viscous lsolutions and adjusting the Viscositythereof. Otherobjects will appearhereinafter.

In accordance With the invention, the `hot `viscous fsolution or liquidto he ycooled is maintained at a temperature above `'the atmosphericlboiling .point of the fluid `or `solvent of the solution, fasfthe casemay be, `and under a pressure at which the fluid -or solvent does notboil. The 1pressureo'n the uid or solution is then suddenly reduced to apressure at Whichthe hot uid boils 1Jiolen'tly Vand expels Volatileportions of the fluid Aor solvent. This expulsion and vaporizationresults in a considerable temperature drop in the remaining fluid orsolution and further cooling can -be accomplished fby condensing theexpelled vapors-ef the volatile uids or solvents and returning Vall or aportion thereof Vto the cooled viscous material. When all of thecondensed 'solvent is returned the ratio of solid and liquidconstituents of the solution is substantially like that in ytheloriginal solution. At this 'point the final viscosity of the liquid orsolution may be adjusted Lby adding -znore or less of the fluid orsolvent lthan Wasinitially present in the hot material. The temperatureof this added or returned solvent may also be regulated in order toregulate the resulting temperature of the solution. If additionalliquids .or solvents areadded, it is preA ierred that they be of thesame lpurity as those resulting Afrom the instant process. The solventsmay .he reincorporated in the solution by a mefchanical stirrer. Thecooled solution is then withdrawn from the tank. This process `can beoperated continuously.

The invention is further illustrated in connection with the attacheddrawing show-ing a schematic View inelevation of apparatus suitable foruse in carrying out the process.

As shown in the vdrawing the Vapparatus comyprises a `solution heater ilin which the solution may loe heated above its boiling point While heing .maintained at a :pressure `at which. boiling carin f place. Whenthe temperature and pressure of the solution is rat a .predeterminedvalue, valve lil in .pipe -line vl l is opened-permitting the .solutionte iiow through a pressure reducing valve lt2 and thence intolcooling`tank i3 which is maintained at va pressure .lower than that in the`heater Tank i3 has associated therewith c Va stirrer i4 whose shaft l5.isattaohed ato-amotor I6 which is mounted on a support II which alsosupports the tank I3. A vapor exhaust pipe I8 is connected adjacent thetop of the tank I3 and leads through condenser I0. If desired, a vacuumpump system not shown may be attached to pipe I8 in order to reduce thepressure in tank VI3 to a sub-atsmospheric pressure. A solution drawoifpipe 2l is attached to the bottom of tank I3 and is for conductingcooled solution to storage, or to the next operation such as a i'llmcoating process, as may be desired. It will be understoodv that ourprocess can operate merely on a difference of pressure and that apressure less than atmospheric in the tank I3 is not required. However,in certain instances itrmay be desirable to operate the process whiletank I3 is at a pressure lower than atmospheric. In either case,

when the -hot solution under high pressure is forced into the lowpressure atmosphere of tank i3 its liquid solvent boils violentlythroughout its mass and the vapors ilow up into the cold condenser I9.This vaporization results in suddenly cooling the solution more or lessuniformly throughout its mass. The mass is further cooled by the returnof the condensed solvent which is reincorporated in the viscous mass bythe stirrer I4. The cooled solution is withdrawn from-the solutioncooler system through pipe 2 i.

lf it is desired to make the solution less viscous additional solventmay be introduced into tank i3 through pipe 20 which connects to pipeiii. The added solvent thus flows through condenser i9 on its way totank I3. The temperature of this added solvent may be adjusted to adesired value byY means not shown prior to the addition to pipe 20. Ifit is desired to increase the viscosity of the solution the condenser Imay be run het or at an intermediate temperature so that all the vaporsdo not condense and return to the tank. Suitable traps not shown forrecovering the uncondensed vapors maybe installed in the exhaust systembefore'the vacuum pump j' is reached. It will be understood that adesired pressure in the heater I0 and a vacuum in the tank I3 may beobtained by appropriate operation of conventional pressure and vacuumapparatus, not shown. Y

The following are typical examples of the method applied to viscouscellulose ester solutions.

Erample 1 A solution of hydrolyzed cellulose acetate was made up usingacetone as the solvent. Such a solution is suitable for use in the dryspinning method for making acetate yarn laments by the method shown inStone Patent 2,000,047 of May 7, '1935. This solution has a viscositylof approximately 100,000 cps. and in order to facilitate iltering it washeated to 200 F. and forced through a lter at a pressure of 100 poundsper `square inch to remove undissolved cellulose acetate and foreignmatter.

Y At'this pressure the acetone in the solution cannot Vaporize.

l passing through the lter it was introduced into the tank I2 throughthe above described pipe system. yTank I3 being maintained atatmospheric pressure now permits the pressure on the solutionV to drop(and a corresponding rise in temperature takes place in the solution)and suba spinnerette to form laments. Other yarn forming solutionsdisclosed in Stone Patentsv 2,000,047 and 2,000,048 both of May 7, 1935,can be advantageously cooled from their solution mixing .temperatures inaccordance with our invention. v

Example 2 A cellulose acetate butyrate lm base coating solution such asdisclosed in Carver Patent 2,322,827 of June 29, 1943, may be cooledfrom aV temperature of 98 C., at which it was heated under a pressure at'which the solvent does not vaporize toV facilitate solution andltering, to a lm coating temperature of 60 C. by our novel process. Thepressure drop was from 125 pounds per square inch to atmospheric. Otherfilm solutions mentioned in this patent may be advantageously handled byour novel cooling method to reduce the temperature of the solution to atemperature at which the solution may be cast or stored.

Example 3 i The cellulose acetate, cellulose acetate propionate, andcellulose acetate butyrate film base solutions disclosed in ,FordycePatent 2,295,280 of September 8, 1942, were advantageously cooled fromthe solution mixing and ltering temperatures to the casting temperaturesby our process. These solutions may be ltered at pressures of 125 poundsper square inch at a temperature of 60 F. at which the solvents do notvolatilize."

The solution was then cooled in accordance with our invention bydropping thepressure to atmospheric in the apparatus illustrated. Y

While the above examples illustrate ourv invention by initially heatingthe solution'under a pressure which is above that of the atmosphere,commonly called atmospheric pressure, it is contemplated that the methodcan also be carried out by initially heating the solution while it isunder a pressure which is equal to or below atmospheric pressure. Insuch event, the pressure of the tank I3 would be made sub-atmospheric bymeans of the vacuum pump system so that a pressure drop would occurpermitting sudden vaporization of the volatile constituentsV in thesolution or uid being treated. An important feature is initially heatingthe solution to a temperature close tothe boiling point of the solutionat the particular pressure maintained in the heater, and then sufcientlyreducing the pressure to a point atV which the temperature of thesolution will be ator above the boiling point at the reduced pressure.By increasing the temperture from which the solution is flashed theamount of condensed solvent is increased and hence its cooling action`when mixed with solution yat-,equilibrium temperature is increased. Inthis method, a solution is cooled to a lower temperature by evaporationof its'solvents `from a higher temperature.

VWe claim:

The method of preparing a highly viscous cellulose acetate' solutioncontaining a low boiling volatile solvent which comprises heating thesolution to a temperature of4200 F. While maintaining `a pressure on thesolution of lbs. per

vsquare inch, at which conditions the solvent will not Volatilize,filtering the solution at'this tern-Y Vperature and'pressure, thenabruptly' releasing the pressure Von the filtered solution therebypermitting" the solvent to vaporize andv consequently to Vcool thesolution, condensing' vthe vaporized solvent and re-incorporatng aportion of the condensed solvent into the cellulose acetate solution toadjust its final viscosity.

RICHARD W. BRUINS. WALKER F. HUNTER, JR.

REFERENCES CITED The following references are of record in the le ofthis patent:

Number 6 UNITED STATES PATENTS Name Date Daniels Nov. 24, 1925 ClarkMar. 30, 1926 Russell Apr. l, 1930 Atwell Oct. 9, 1934 Gay July 7, 1936Boutwell July 18, 1944

